1. Field of the Invention
This invention relates to a process for separating oxygen from an oxygen-containing gas, such as air. In one aspect, the invention relates to a process in which the oxygen is separated from the oxygen-containing gas by means of a Bi-containing mixed metal oxide membrane. In another aspect, the invention relates to a process for providing an oxygen-consuming substance with oxygen extracted from an oxygen-containing gas by means of a Bi-containing mixed metal oxide membrane.
2. Description of the Prior Art
Bi-containing mixed metal oxide membranes are known. For example, DiCosimo et al. teach in U.S. Pat. No. 4,571,443 a Bi-containing, mixed metal oxide catalyst membrane of the empirical formula EQU BiL.sub.a M.sub.b O.sub.x
where
L is at least one of Y, V, Nb, Ta, W, Mo, Pb, La, Nd, Sm, Er, Yb, Dy and Gd; PA1 M is at least one of Ca, Ba and Sr; PA1 a is 0-1; and PA1 b is 0-0.1 PA1 (a) an oxide of cobalt, PA1 (b) an oxide of at least one metal selected from strontium and lanthanum, and PA1 (c) an oxide of at least one metal selected from bismuth and cerium. PA1 A is at least one of La, U, Th, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Mg, Ca, Sr and Ba; PA1 M is at least one of Sc, Ti, Cr, Mn, Fe, Ni, Cu and Zn; PA1 M' is at least one of Co, Rh, Pd, Pt and Ru; PA1 x and y are individually a number between about 0.01 and about 10; PA1 z is a number of 0 to about 0.2; and PA1 n is a number that satisfies the valence requirements of the other elements present; PA1 (i) oxygen is extracted from the first oxygen-containing gas at the first surface of the membrane; and PA1 (ii) the extracted oxygen is transported across the membrane, in the form of oxide ions, to the second surface of the membrane; and
These catalyst membranes are used to extract oxygen from an oxygen-containing gas, such as air, and deliver it to substrates, such as propylene, which react with the oxygen in the presence of the catalyst membrane to form dimers and other products. However the best oxygen flux reported for these catalyst membranes was 27 milliamperes per square centimeter (27 mA/cm.sup.2) at 600.degree. C.
Yoshisato et al. teach in U.S. Pat. No. 4,330,633 a solid electrolyte having electron conductivity and oxide ion conductivity, the electrolyte consisting substantially of
The electrolyte is taught as being useful for separating oxygen from a gaseous atmosphere having a high oxygen partial pressure into a gaseous atmosphere having a low oxygen partial pressure. For a sintered body consisting of 25 mol % of cobalt oxide, 32.5 mol % of lanthanum oxide, and 42.5 mol % of bismuth oxide, the oxygen flux at 800.degree. C. was 51 mA/cm.sup.2.
Takahashi et al. teach in their article entitled "Oxide Ion Conductors Based on Bismuthsesquioxide", Materials Research Bulletin, Vol 13, pp 1447-1453 (1978) oxide ion conductive solid electrolytes based on bismuthsesquioxide. While these materials have high oxide ion conductivity, they are electronic insulators and thus require an external circuit to return electrons to the oxide source.
While these references and others teach various Bi-containing mixed metal oxides, none teach such compositions as having commercially significant oxide ion flux (greater than about 100 mA/cm.sup.2), particularly at relatively low temperatures (less than about 900.degree. C.). significant oxide ion flux (greater than about 100 mA/cm.sup.2), particularly at relatively low temperatures (less than about 900.degree. C.).